1. Field of the Invention
The present invention relates to a hand-held power tool for rotatably driving a working tool, in particular, a combustion-engined concrete cutting and grinding power tool including a drive belt and a belt tensioning device located between two arms longitudinally displaceable relative to each other and carrying respective deflection rollers of the drive belt.
2. Description of the Prior Art
Because the drive belt is subjected to fatigue and wear during its intended use, it becomes stretched, which requires a regular aftertensioning by lengthening the drive path, e.g., increasing the distance between the two deflection rollers. Necessarily, after a manual release of the locking means, the actual aftertensioning of the drive belt requires a complete control of the user. Generally, and optimal belt tensioning can be determined by using appropriate textbook or manual recommendations. However, practically, it cannot be reliably established.
Automatic belt tensioning devices with a preloaded spring are known and are disclosed, e.g., in German Publications DE 746 011 and DE 198 49 886. U.S. Pat. No. 3,606,707 discloses a combustion-engined concrete cutting and grinding power tool in which a semi-automatic (i.e., after a manual release of the locking means) belt tensioning device provides for an optimal belt tensioning with a preloaded compression spring arranged between two telescopic arms. Then, both arms are locked with respect to each other, using clamping screws.
German Publication DE 38 41 644 discloses a combustion-engined concrete cutting and grinding power tool with a semi-automatic belt tensioning device that provides an optimal belt tensioning, using a compression spring preloaded against the first arm and which tensions a pull rod displaceable coaxially in the interior of the belt tensioning device and eccentrically connected with a rotary setting device that rotates within the second arm. When the rotary setting device is manually rotated against the biasing force of the compression spring and moves toward the stop over the near dead point of the mutual longitudinal displacement of the arms, the compression spring becomes preloaded against the stop. Thereby, the arm becomes longitudinally and tension-free displaceable, which makes replacement of the drive belt possible.
An object of the present invention is to provide a hand-held power tool with a simplified semi-automatic belt tensioning device.